Adjustable length tap and method for drilling and tapping a bore in bone

ABSTRACT

The present invention is directed to an adjustable self drilling tap assembly and method for drilling and tapping bores in bone for use in orthopedic procedures to treat bone. The adjustable length tap assembly includes a shaft having cutting threads for drilling holes in bone, a stop collar configured and dimensioned to be translatable along the longitudinal axis of the shaft, and a locking collar comprising a member configured and dimensioned to be received over at least a portion of the stop collar. The locking collar preferably is configured and dimensioned to engage with the stop collar to adjustably set the effective length for the cutting threads and to prevent movement of the stop collar along the longitudinal axis of the shaft.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation of U.S. patent application Ser. No. 11/221,546filed Sep. 7, 2005 now U.S. Pat. No. 7,569,058, entitled “AdjustableLength Tap and Method for Drilling and Tapping a Bore in Bone”, which isa divisional of U.S. patent application Ser. No. 10/292,515 filed Nov.13, 2002 now U.S. Pat. No. 6,951,562, entitled “Adjustable Length Tapand Method for Drilling and Tapping a Bore in Bone”, the contents ofwhich are incorporated herein by reference in their entirety.

FIELD OF THE INVENTION

The present invention is directed to a self-drilling tap and its methodfor use in orthopedic procedures to treat bone, and in particular to adevice and method for drilling and tapping holes in bone to accommodatescrews used in cranio-facial, mandible, pelvic and other orthopedicprocedures.

BACKGROUND OF THE INVENTION

Drilling in bones, particularly bones of the face and head, requiresaccurate and reliable control over the penetration depth. For instance,over drilling and tapping a bore may damage the brain or otherunderlying soft tissue. To reduce this risk, self-drilling taps for usein cranio-facial procedures generally have a fixed depth. There exists aneed for a self-drilling tap having an adjustable length, which mayaccurately and reliably replace several taps of various fixed lengths.

SUMMARY OF THE INVENTION

The present invention is directed to a tap assembly which may beadjusted by a user to drill and tap holes in bone in order toaccommodate screws of various lengths. The adjustable length tap maycomprise a shaft, a stop collar and a locking collar, which cooperate toexpose and set an effective length of cutting threads located on the tipof the shaft.

The shaft preferably has a longitudinal axis, a proximal end, and adistal end with cutting threads for drilling and tapping holes in bone.The adjustable length tap assembly may also include a stop collar havingproximal and distal ends. The distal end of the stop collar ispreferably configured and dimensioned to provide a stop for the selfdrilling tap. The stop collar preferably is configured and dimensionedto be translatable along the longitudinal axis of the shaft. The shaftpreferably includes length indicator marks, the length indicator marksbeing configured and dimensioned to allow for a controlled setting ofthe effective length of the adjustable length tap assembly. Each lengthindicator mark is preferably configured and dimensioned to correspondwith one effective length. In addition, each length indicator mark ispreferably configured and dimensioned to be visibly aligned with theproximal end of the stop collar, when the effective length is set. In anexemplary embodiment, each length indicator mark is selectively disposedon the shaft, and each length indicator mark is visibly identified byindicia. The shaft is preferably made from biocompatible materials andmay be made from non-magnetic materials.

The stop collar has a body having an inner surface and an outer surface.A portion of the inner surface is preferably configured and dimensionedto engage with the shaft in at least one predetermined location. Thestop collar preferably has one or more fingers, and the shaft preferablyhas one or more grooves. In addition, the one or more fingers may haveinner and outer surfaces and at least one projection or nub formed onthe inner surface. The projection preferably is configured anddimensioned to interact with the grooves to prevent translationalmovement of the stop collar along the longitudinal axis of the shaft.The one or more fingers preferably is formed by at least two slots. Eachof the two slots preferably extend from the outer surface of the stopcollar to the inner surface of the stop collar. Preferably, the stopcollar has at least two fingers, the fingers being substantiallyidentical and arranged in a substantially symmetrical configurationabout a central axis of the stop collar.

In an illustrative embodiment, the at least one projection on the stopcollar has a mid-point, and the at least one groove on the shaft has amid-point. A first distance measured from the mid-point of the at leastone projection to the proximal end of the stop collar preferably isrelated to a second distance measured from the mid-point of the at leastone groove to a corresponding length indicator mark on the shaft. Thefirst distance preferably is substantially equal to the second distance.The grooves preferably extend continuously about the shaft, and thegrooves preferably are oriented substantially perpendicular to thelongitudinal axis of the shaft. In an exemplary embodiment, the groovesare substantially equidistant from one another. The grooves may also besubstantially identical in size and shape.

The adjustable length tap assembly also comprises a locking collar. Thelocking collar preferably is configured and dimensioned to be receivedover at least a portion of the stop collar. The locking collar ispreferably configured and dimensioned to engage with the stop collar toset the effective length of the cutting threads, and preferably toprevent movement of the stop collar along the longitudinal axis of theshaft. The locking collar, also, is preferably configured anddimensioned to bear against a structure on the outer surface of the oneor more fingers to releasably engage the at least one nub with a grooveon the shaft. The locking collar preferably comprises a tubular memberhaving a bore, and the proximal end of the locking collar preferably iscapable of translating over the proximal end of the stop collar. In anexemplary embodiment, at least a part of the locking collar istransparent, and the locking collar preferably is formed from a medicalgrade poly-carbonate.

In use, the locking collar and the stop collar preferably engage or matewith each other in at least two configurations, a first configurationwhich allows transnational movement of the stop collar and lockingcollar together along the shaft, and a second configuration thatprevents translational movement of the stop collar along thelongitudinal axis of the shaft. The stop collar and locking collar,generally, are free to rotate about the shaft when the stop collar andlocking collar engage in the second configuration.

The present invention is also directed to a surgical kit for drillingand tapping holes in bone. The kit preferably comprises one or moreshafts each having a longitudinal axis, a proximal end and a distal end.At least a portion of each shaft should have cutting threads fordrilling and tapping bores in bone. The kit may also include a stopcollar having proximal and distal ends, which preferably is configuredand dimensioned to be translatable along the longitudinal axis of eachof the shafts. The stop collar preferably has a body having an innersurface and an outer surface, at least a portion of the inner surfacebeing configured and dimensioned to engage with the at least one shaftin at least one predetermined location. Additionally, the kit mayfurther include a locking collar comprising a member configured anddimensioned to be received over at least a portion of the stop collar.The locking collar preferably is configured and dimensioned to engage ormate with the stop collar to set at least one effective length for thecutting threads and preferably to prevent movement of the stop collaralong the longitudinal axis of the at least one shaft.

The invention also relates to a method for drilling and tapping a borein bone. The method preferably comprises selecting a bone fasteningelement having a screw thread, and selecting a self-drilling tap havinga longitudinal axis and cutting threads. Preferably, the cutting threadsare located on the distal end of the self-drilling tap and are adaptedto create and tap a bore in bone for receiving the selected screwthread. The method preferably includes mounting a stop collar on thetap, positioning a locking collar on the tap, passing at least a part ofthe locking collar over the proximal end of the stop collar, and joiningthe stop collar with the locking collar. The method preferably comprisespositioning the stop collar in at least one predetermined location whichmay cover at least a part of the cutting threads, verifying the locationof the stop collar by visually inspecting the location of the proximalend of the stop collar relative to the self-drilling tap, and lockingrelative movement of the self-drilling tap, stop collar, and lockingcollar along the longitudinal axis. The method preferably includesplacing the cutting threads on bone, rotating the self-drilling tap toadvance the cutting threads into bone, forming a tapped bore in bone,contacting the stop collar against a surface to block advancement of theself-drilling tap, and removing the self-drilling tap from the bore. Themethod may further include advancing the screw thread into the bore tofix the bone fastening element in bone.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred features of the present invention are disclosed in theaccompanying drawings, wherein similar reference characters denotesimilar elements throughout the several views, and wherein:

FIG. 1 shows a perspective view of an exemplary embodiment of theadjustable length tap assembly.

FIG. 2 shows a partial cross-sectional view along line 2-2 of FIG. 1;

FIG. 3 shows a plan view of the shaft of the tap assembly of FIG. 2;

FIG. 4 shows a partial plan view of the reverse side of the of shaft ofFIG. 3;

FIG. 5 shows an enlarged view of grooves and markings on the shaft ofFIG. 3;

FIG. 6 shows a perspective view of the stop collar of the tap assemblyof FIG. 1;

FIG. 7 shows a cross-sectional view along line 7-7 of FIG. 6;

FIG. 8 shows an enlarged plan view of a slot of the stop collar of FIG.6;

FIG. 9 shows an enlarged view of a nub and seating projection on thestop collar of FIG. 6;

FIG. 10 shows a front elevation of the locking collar shown in FIG. 1;

FIG. 11 shows a cross-sectional view along line 11-11 of FIG. 10;

FIG. 12 shows a partial cross-sectional view along the longitudinal axisof another embodiment of the tap assembly of FIG. 1;

FIG. 13 shows a cross-sectional view of the locking collar along thelongitudinal 25 axis of the tap assembly of FIG. 12;

FIG. 14 is a perspective view of an exemplary collection of instruments,which in use, may form an adjustable length tap assembly of FIG. 1; and

FIG. 15 is a plan view of an illustrative kit housing the collection ofinstruments of FIG. 14.

DETAILED DESCRIPTION OF THE EMBODIMENTS

In the description that follows, any reference to either orientation ordirection is intended primarily for the convenience of description andis not intended in any way to limit the scope of the present inventionthereto.

FIG. 1 shows an assembly 10 for use in drilling and tapping holes inbone. The assembly 10 comprises a self-drilling tap 12 having alongitudinal axis 14, a stop collar 18, and a locking collar 20. Theself-drilling tap 12 may have a distal end 13 with cutting threads 16adapted to drill and tap holes in bone. The stop collar 18 and lockingcollar 20 may be moved along the self-drilling tap 12 to expose aportion of the cutting threads 16. The relative position of stop collar18 and locking collar 20 may be fixed along the longitudinal axis 14 ofthe self-drilling tap 12. The stop collar 18 and the locking collar 20may be free to rotate about the longitudinal axis 14 of theself-drilling tap, even though translational movement along thelongitudinal axis 14 is prevented. The assembly 10 may to be used withother instruments such as a handle and guide plate (not shown) to drilland tap holes in bone. Detachable handles, guide plates, and drills arerepresentative of the instruments and other devices that may be used inconjunction with the adjustable length tap assembly. These instruments,however, may not always be required or may be replaced by differentdevices that perform similar, additional, or different functions.

FIG. 2 shows a cut away view of the adjustable length tap assembly. Thestop collar 18 and the locking collar 20 are shown in cross-section, andthe shaft 22 is shown in plan view. As shown in FIG. 2, theself-drilling tap 12 includes a shaft 22 having a tip or distal end 13with cutting threads 16. The tap 12 further comprises a plurality ofcircumferential grooves 24, indica 26, such as for example lines, formarking the effective length 28 of the exposed portion of the cuttingthreads 16, and a coupling element 30 for connecting the self-drillingtap 12 to a handle or a drill (not shown) at the proximal end 31thereof.

The maximum outer diameter 32 of the cutting threads 16 and the length34 of the tip 13, which contains the cutting threads, may be fixed. Thedimensions of the tip 13, for any particular tap 12, may be based on thesize and length of the screw for to be inserted in the bore. Thedimensions of the tip 13 may further be adapted to accommodate thethickness of a guide plate. For instance, a special screw may bedeveloped for use in a pelvic procedure, for example, and the dimensionsof the tip 13 of the self-drilling tap 12 may be designed to accommodatethat screw. For example, one screw type may have an outer diameter of1.5 mm and a length of 3 mm, and the dimension of the tip 13 may beconfigured and dimensioned to create a tapped bore that is adapted forscrews of that type. Other non-limiting examples of screws, for whichthe self-drilling tap 12 may be dimensioned, include screws having anouter diameter from about 2.0 mm to about 4.0 mm and having a lengthfrom about 3.0 mm to about 8.0 mm. As one skilled in the art wouldreadily appreciate, a self-drilling tap may also be developed for largeror smaller screws.

The cutting threads 16 may be particularly adapted to cut and removebone without damaging adjacent tissue. The threads may include sharpcutting flutes 36 and one or more straight flutes 38 for removing bonechips and cuttings from the bore. For example, two straight flutesaligned 180° from each other may be disposed on the tip. One of ordinaryskill in the art would readily appreciate that the number andconfiguration of cutting flutes 36 and straight flutes 38 may be widelyvaried, or in addition to or alternatively a wide variety of otherconfigurations and combinations may be used.

The shaft 22 of the tap 12, preferably, may have an outer diameter 40that is operably configured and dimensioned to slidably receive the stopcollar 18 and the locking collar 20. A set of taps which may be adaptedfor screws having differing predetermined diameters and lengths,preferably may each have a shaft 22 of same diameter 40. In an exemplaryembodiment, the outer diameter 40 of the shaft 22 may be about 3.0 mm.As one skilled in the art would readily appreciate, a set ofself-drilling taps having different tip configurations may be suppliedas a kit for use with one stop collar 18 and one locking collar 20. Morethan one stop collar 18 and more than one locking collar may also besupplied in the kit. For example, a set of taps 12 having a differentouter diameter may be supplied which would be used with different stopand locking collar combinations.

Referring to FIGS. 3-5, the shaft 22 may further comprise two or moregrooves 24. The grooves 24 may be spaced from the tip 13 on the middleportion of the tap 12. Each groove 24 mayor may not extend continuouslyabout the shaft 22. In an illustrative embodiment of a self-drilling tap12 there may be six grooves 24 spaced equidistant from one another andoriented perpendicular to the longitudinal axis of the shaft 22. Asshown in FIG. 5, the radius 42 (i.e., the distance equal to one-half thegroove width 44) of each groove 24 preferably may be substantiallyconstant. In addition, each groove preferably may have substantially thesame radius 42. Similarly, the diameter 46 of the grooves 24 may vary,but in a preferred embodiment are the same. The radius 42 and diameter46 of each groove 24 may be operably configured and dimensioned tocooperate with at least one detent or nub 48 on the stop collar 18, asshown in FIG. 2. Engagement of a nub or projection 48 with a groove 24may be used to set the position of the stop collar along the length ofthe shaft 22 and thus set the penetration or effective length 28 of theadjustable tap assembly 10. As described in further detail below, a usermay selectively press the nubs of the stop collar 18 into a groove 24 onthe shaft to lock the penetration or effective length 28 of theadjustable tap assembly.

As shown in FIG. 5, a tap 12 having a shaft 22, for example, with anouter diameter 40 of about 3.0 mm may have grooves 24 having a diameter46 of about 2.6 mm and a radius 42 of about 0.3 mm. Each groove 24 maybe spaced one from another at a fixed interval, for example, 1.0 mm oncenter. As one skilled in the art would readily appreciate, other grooveconfigurations may be desirable. In general, however, a set ofself-drilling taps adapted for screws of different diameters, aspreviously described, may have substantially identical grooves andgroove patterns so as to provide the user of the tool with a uniformfeel when setting the penetration or effective length 28 of theadjustable tap assembly 10. A standard feel for setting the effectivelength 28 of the adjustable tap assembly 10 may promote ease,reliability, and accuracy in the selection of a desired effective taplength 28 during a surgical procedure.

Indica 26 or length indicators may be marked on the shaft 22perpendicular to the longitudinal axis 14 of the self-drilling tap 12.In general, one length indicator 26 may be marked on the shaft 22 foreach groove 24. Each length indicator 26 may indicate the length of thescrew for which a bore is to be drilled. Alternatively, the lengthindicator 26 may correspond to some other designation for a particularscrew type. In general, the distance between the mid-point of one groove24 and a corresponding length indicator 26 may correspond with thedimensions of the stop collar 18 to allow for the controlled andaccurate setting of a predetermined tap length 28. For example, thedistance 52 between the mid-point of a groove 24 and a correspondinglength indicator 26, may be the same length as the distance 73, shown inFIG. 7, which is measured between the mid-point of the nub 48 and theend 54 of the stop collar.

Referring back to FIGS. 2-5, length indicators 26 may be selectivelymarked on the shaft 22. For instance, the length indicators for screwshaving odd number designations may be marked on one side of the shaft,and length indicators for screws having even number designations may bemarked on the other side of the shaft. Such a marking pattern mayfacilitate the selection of a desired effective length 28 by making iteasier to identify, select, and confirm the adjustment. Moreover, eachlength indicator 26 may be identified by indica 56 which uniquelysignify each possible tap length 28 selection. For instance, the indica56 may comprise numerals which relate to the length or type of screw forwhich a bore is to be drilled and tapped. In an illustrativeconfiguration, the indica 56 may be numerals which are bisected by theassociated length indicators 26. This configuration may provide forlarger numerals and clearer identification of the associated lengthindicator. Markings 26, 56 may be laser etched into the shaft.

The self-drilling tap 12 may be adapted for use with an integrallyformed handle (not shown). Alternatively, the proximal end of theself-drilling tap 31 may be adapted for 35 connection to a removablehandle or drill (not shown). For instance, the self-drilling tap 12 mayhave a hex coupling for connecting to a handle for use as a manuallyoperated instrument. The tap 12 might also be adapted for quick couplingto a drill. In general, the tap may be made from materials which arebio-compatible and possess relatively high mechanical durability. Forexample, the tap may be integrally formed from a blank made fromstainless steel. In a preferred embodiment, the tap may be made from 440A stainless steel. The tap may also be made from non-magnetic materialsso that it may be suitable for use with an MRI system. The tap may alsobe radiolucent, or portions may be radiolucent.

FIG. 6 shows a perspective view of the stop collar of FIG. 1. Aspreviously described, the stop collar 18 is operably configured anddimensioned to cooperate with the shaft 22 and locking collar 20 to setand fix the penetration or effective length 28 of the adjustable lengthtap assembly 10. The stop collar shown in FIG. 6 has a nose 58 at thedistal end 60, a fore-collar 62 adjacent the nose 58, an abutment ring64, connecting elements 66 for coupling with the locking collar 20, anda plurality of fingers 68 for engaging with the shaft 20.

The nose 58 may be configured and dimensioned to provide a secure stopfor the self-drilling tap 13 and may have an outer dimension close tothe dimensions of the shaft to reduce visual obstruction of the tip 13when the adjustable length tap assembly 10 is positioned for drilling.The outer dimension of the stop collar may then flare outward graduallyto a second or intermediate outer-dimension at the fore-collar 62 toprovide a surface which may be readily gripped and manipulated by auser. Thus, the profile of nose 58 and fore-collar 62 may be configuredand dimensioned to reduce the likelihood of incorrect seating of theadjustable length tap assembly 10 on a drill plate and/or bone.

The fore-collar 62 may further include a transition to a portion havinga larger outer dimension which may form an abutment ring 64. Theabutment ring 64 may be operably configured and dimensioned to provide astop 70 for the locking collar 20, which may be connected to the stopcollar 18 by connecting elements 66 located near the abutment ring 64.In FIG. 6, the connecting elements 66 comprise external threads whichare disposed about the central portion of the stop collar 18 between theabutment ring 64 and a plurality of fingers 68. Coupling elements otherthan threads may be used to couple the locking collar 20 with the stopcollar 18.

The fingers 68 assist in fixing the position of the stop collar and mayeach generally comprise an elongated member, that is formed by slots 72in a thin wall section of the stop collar 18. The fingers 68 areconfigured and dimensioned to flex. In FIG. 6, the stop collar 18 hasfour fingers 68. As one of skill in the art might appreciate, a stopcollar 18 having a configuration with less or more fingers 68 might alsobe used. For example, a stop collar having three fingers defined bythree slots may be used, or a stop collar with five fingers and havingfive slots may be used. The fingers 68 may be substantially identical inconstruction or they may differ one from another. Similarly, the fingers68 may be disposed in a substantially symmetrical configuration or theymay be disposed about the stop collar in some other fashion. Forinstance, in the embodiment shown in FIGS. 6-9, the stop collar 18comprises four substantially identical fingers 68 disposed in agenerally symmetrical pattern about the proximal end 74 of the stopcollar 18.

As shown in FIGS. 7 and 9, the inner surface 78 of the fingers 68 may besmooth and may be configured and dimensioned to bear upon and slidealong the shaft 22 of the self-drilling tap 12. The fingers 68 of thestop collar 18 may also be operably configured and dimensioned toselectively engage and disengage with the grooves 24 of the tap 12. Forexample, this may be accomplished by a projection, structure or nub 48located on the inner surface 78 of each finger 68.

The outer surface 76 of each finger 68 may be configured and dimensionedto slidably receive the locking collar 20 over the outer surface 76. Theouter surfaces 76 of the fingers 68 also may be configured anddimensioned to bear against the locking collar 20. This may beaccomplished by a structure, as shown in FIGS. 8 and 9, such as a raisedarea or seat 80, located on the outer surface 76 of each finger 68. Ingeneral, as the locking collar 20 is advanced over the stop collar 18,the locking collar may press against the seat 80 and drive the nub 48into engagement with a groove 24 on the shaft 22 of the self-drillingtap 12. The nub 48, for example, may be substantially triangular ortrapezoidal in section. The shape of the nub 48 may be designed tosecurely engage with the groove 24 when locking the penetration oreffective length 28 of the adjustable length tap assembly 10. The shapeof nub may also be configured to facilitate disengagement of the nub 48from a groove 24 when unlocking or adjusting the effective length 28 ofthe adjustable length tap assembly 10.

Referring to FIG. 8, the number and geometry of the slots 72 may beconfigured and dimensioned to provide the fingers 68 with specialproperties. For instance, a slot 72 comprising an enlarged roundedportion 82 at the base may be formed to provide special properties tothe finger. The enlarged rounded portion 82 may provide increasedflexibility while preventing stress concentrations and fatigue. Also,one or more slots 72 may be adapted to provide increased resiliency orflex to the fingers 68, making it easier to slide the stop collar 18along the shaft 22, as the nubs 48 engage and disengage with the grooves24.

The stop collar 18 may be formed from materials which arebio-compatible, and which are capable of withstanding the requiredmechanical loading and abrasion. For example, the stop collar 18,preferably may be made from materials that are durable and will preventshearing of the nubs. In addition, the stop collar may be made frommaterials which provide the fingers with added resiliency to movementyet will not readily fatigue or fail during use. In addition, the stopcollar 18 preferably may be made from materials which will not fail whenplaced into abrasive contact with a drill guide plate during use. Thus,for example, the stop collar 18 preferably may be made from any 300series stainless steel. Preferably, 316 stainless steel may be used toform the stop collar 18. Other non-limiting examples of materials fromwhich the stop collar may be formed in include titanium andtitanium-alloys. The stop collar 18 might also be formed from materialswhich are non-magnetic in order to provide a tap assembly 18 which issuitable for use with an MRI system. The stop collar may also beradiolucent, or portions may be radiolucent.

Referring to FIGS. 10 and 11, the locking collar 20 generally comprisesa tubular member having a bore 86, which is configured and adapted toengage or mate with the stop collar 18. The locking collar 20 maycontrol the movement of the tap assembly. The cross-section of thelocking collar 20 taken in a direction perpendicular to the longitudinalaxis 14 of the locking collar may be substantially uniform.Alternatively, the locking collar 20 may have a cross section thatvaries. For example, the shape of the exterior surface 84 may beconstant and the shape and diameter of the interior bore 86 may varyalong the length of the locking collar. In another example, the shape ofthe exterior surface 84 may vary and the bore 86 may remainsubstantially unchanged along the length of the locking collar 20. Inthe embodiment shown in FIGS. 10 and 11, the locking collar is agenerally hollow cylinder.

In general, the bore 86 of the locking collar 20 may be configured anddimensioned to slide along the tap 12 as well as over the fingers 68 ofthe stop collar 18. The cross-section of the bore 86 may be circular,polygonal or some other shape. In addition, the dimensions of the bore86 may vary, and part of the bore 86 may be adapted to connect with thestop collar 18. For example, the distal end 88 of the bore 86 maycomprise internal screw threads 90. Additionally, the bore 86 of thelocking collar 20 may comprise sections having different dimensions. Inparticular, the locking collar may have a bore 86 comprising multiplesections of progressively smaller dimension. For instance, thedimensions of the bore may be greater at the distal end 88 than at theproximal end 92 of the locking collar 20. such that the progressivechange in dimensions of the bore 86 presses the fingers 68 of the stopcollar 18 more firmly into the grooves 24 of the shaft 22 when thelocking collar 20 and stop collar 18 are coupled and tightened.

The exterior surfaces 84 of the locking collar 20 may also facilitatequick, reliable and accurate adjustment of the exposed tap length 28. Inthe embodiment of FIGS. 10 and 11, the dimension of the exterior surface84 tapers gradually from the distal end to the proximal end. The lockingcollar 20 may be thicker at the distal end 88 to accommodate internalcoupling elements 90 (for example, internal screw threads) which areadapted to engage or mate with connecting elements 66 (for example,external screw threads) on the stop collar 18. The locking collar 20also may be thicker in the distal end 88 to provide a comfortablegripping section 94 so that the locking collar 20 may be reliably heldand manipulated.

The exterior surface 84 of the locking collar 20 may further compriseraised areas 96 to enhance the grip and tactile feel of the lockingcollar 20. In addition, the raised areas 96 may promote the ease andreliability of setting and locking the length 28 of the tap assembly. InFIGS. 10 and 11, these raised areas 96 are in the form of longitudinalridges that are radially disposed about the outer surface 84 of thelocking collar. Other grip enhancing configurations on the exteriorsurface 84 might also be envisioned by one of ordinary skill in the art,such as for example, circumferential raised areas or ridges, orcombinations of longitudinal and circumferential ridges, or othersurface texturing.

The proximal end 92 of the locking collar 20 may have a thinner wallsection than at the distal end 88 to enhance visibility through thelocking collar 20 when looking at markings on the shaft 22. A thinnerwall section may also enhance visibility through these areas of thelocking collar 20. A relatively thin wall section at the distal end 88may also enhance visual clarity along the shaft 22 and through openingsor windows that may be formed in the locking collar 20. For instance,the proximal end 92 (i.e. the finger tips) of the locking collar 20 mayalign with the selected length indicator 26 for a desired tap length 28.In another example, the selected tap length indicator 26 and indica 56may be visible through an opening or window in an opaque locking collar20.

In FIGS. 10 and 11, the proximal end 92 of the locking collar 20 maycomprise a clear material, which may be substantially transparent. Thevisibility provided by such a material may allow a user to see directlythrough the locking collar 20 and easily view the length indicators 26,indica 56, and the proximal end 92 of the stop collar 18 to visuallydetermine the effective length 28 of the adjustable-length tap assembly.The clear material may or may not have a tint. One clear material fromwhich the locking collar may be made is plastic. In particular, thelocking collar 20 may be configured and dimensioned to be fabricated asa molded piece. A locking collar 20 formed from plastic may haveconnecting elements 90 (for example, threads) for connecting to the stopcollar 18 which may be made from other materials. In a preferredembodiment, the molded locking collar 20 may be made from a medicalgrade poly-carbonate. For example, the locking collar may be formed from“MAKROLON.”™ In general, plastic materials that may be used for formingthe locking collar 20 should be able to withstand gamma-sterilizationduring packaging. The locking collar 20 may also be made from otherbio-compatible materials, including the same materials described abovein connection with the shaft and stop collar.

Referring to FIGS. 12 and 13, in another embodiment of the adjustablelength tap assembly 98, the locking collar 99 may be speciallyconfigured and dimensioned to be formed from a metal-alloy such as 316stainless steel. As shown in FIG. 13, the locking collar 99 may comprisea cylinder having a bore 100 of varying dimension, which extends fromthe distal end 101 to the proximal end 102. As shown in FIG. 12, thelocking collar 99 may be capable of sliding completely over the proximalend 103 of the stop collar 104, when coupled to the stop collar, therebyproviding an unobstructed view of the length indicators. Thus, thelocking collar 99 mayor may not have windows or slots to allow a user toread the setting of effective length 28 of the adjustable length tapassembly 98.

FIG. 14 shows an exemplary collection of instruments 104, which may beincluded in a pre-packaged surgical kit 106 (shown in FIG. 15) forforming an adjustable length tap assembly 12 that may be used to drilland tap bores in bone. The instruments 104 preferably may include a stopcollar 18, a locking collar 20, and more than one tap 12. The collectionof instruments 104 preferably may also include a handle (not shown) forreleasably securing to each tap 12, so that a user may manually drilland tap bores in bone. In the illustrative embodiment shown in FIG. 14,three taps 12 are included in the collection 104. The taps 12 preferablymay be used interchangeably with the stop collar 18 and the lockingcollar 20. The taps 12 preferably may also have identical shaft 22 andgroove configurations 24. The taps 12 may further have cutting threads16 that are adapted for screws of a similar type but of differentdiameter. Alternatively, the taps may have cutting threads 16 ofsubstantially identical size and shape, or the cutting threads 16adapted for different types of screws. It should be appreciated that awide variety of various instruments may be contained in the kit 106. Forexample, a first kit may package a collection of instruments adapted fora particular mandible procedure, a second kit can package a collectionof instruments adapted for a particular pelvic procedure, and a thirdkit may package a collection of instruments for a particular orthopedicprocedure. FIGS. 14 and 15 illustrate one of many different possibleembodiments for the instrument collection 104 and kit housing 106.

Referring to FIG. 15, in the illustrated embodiment, the kit 106includes an interior tray 108 made, e.g., from die cut cardboard,plastic sheet, or thermo-formed plastic material. The tray 108 mayinclude spaced apart tabs or the like (not shown), which may hold thevarious instruments 104 in a secure position during sterilization andstorage prior to use. When packaged as a sterile assembly, the kit 106may include an inner wrap 110, which is peripherally sealed by heat orthe like, to enclose the tray 108 from contact with the outsideenvironment. One end of the inner wrap may include a conventionalpeal-away seal 112, to provide quick access to the tray 108 at theinstant of use, which preferably occurs in a sterile environment, suchas within an operating room. When packaged as a sterile assembly, thekit 106 may also include an outer wrap 114, which is also peripherallysealed by heat or the like, to enclosed the inner wrap 110. One end ofthe outer wrap may also include a conventional peal-away seal 116, toprovide access to the inner wrap 110 and its contents. The outer wrap114 can be removed from the inner wrap in anticipation of imminent use,without compromising sterility of the contents of the kit 106.

Each inner and outer wrap 110 and 114 may include a peripherally sealedtop sheet 118 and bottom sheet (not shown). In the illustratedembodiment, the top sheet 118 preferably may be made of transparentplastic film, like polyethylene or MYLAR.™ material, to allow visualidentification of the contents of the kit 106. The bottom sheet may bemade from a material that is permeable to ETO sterilization gas, suchas, for example, TYVEK™ plastic material. The kit 106 may also includein the tray 108 directions 120 for using the contents of the kit 106 tocarry out a desired procedure. An exemplary procedure which thedirections 120 can describe will be explained later. When packaged as asterile assembly, the directions 120 may also include a statement, forexample, “For Single Patient Use Only” (or comparable language) toaffirmatively caution against reuse of the contents of the kit 106 whoseperformance characteristics and efficacy may degrade after use. Theadjustable length tap assembly 20, for these reasons, may be used butfor a single surgical procedure and then discarded. The directions 120may also affirmatively instruct against resterilization of a portion orall of the contents of the kit 106, and also may instruct the physicianto dispose of at least these contents of the kit 106 upon use inaccordance with applicable biological waste procedures. The presence ofthe collection of instruments 104 packaged in the sterile kit 106 mayverify to the physician that the contents are sterile and have not beensubjected to prior use. The physician may thereby be assured that theinstruments 104 meet established performance and sterilityspecifications.

In use, the locking collar 20 slips over the stop collar 18 and tap 12and when tightened to the stop collar 18, locks the assembly 10. Thelocking may be accomplished by nubs 48 on the fingers 68 of the stopcollar 18 being driven into grooves 24 on the shaft 22. The proximaledge of the fingers (i.e., the finger tips) 88 may align with the lengthindicator 26 on the tap shaft 12 that corresponds with the groove 24 thenubs 48 engage. Once the stop collar 18 and the locking collar 20 arecoupled together, the degree of engagement between the nubs 48 and thelocking grooves 20 may be controlled. The degree of engagement betweenthe grooves 24 and the nubs 48 may vary by design from a firm engagementto loose engagement. When loosely engaged the stop collar 18 and thelocking collar 20 may be moved in unison along the shaft 22 in a ratchetlike fashion. To promote a secure connection between the stop collar 18,the locking collar 20, and the shaft 22, the fingers 68 of the stopcollar 18 have a raised area 80 on the outer surface 76 to cause the nub48 on the inner surface 78 to be pushed firmly into engagement with thegroove 24. The stop collar 18 and locking collar 20 preferably arecapable of resisting, without axial movement, an axial force of at leastabout 300 N, when the adjustable length tap assembly is locked.

The adjustable length tap assembly 10 is directed toward a method fordrilling and tapping holes in bone. Initially, a user selects a tap 12for preparing a bore which is adapted for a particular screwconfiguration. The selection may be based, for instance, on the screwdiameter, or the part number of the screw. A stop collar 18 then may bemounted about the tap 12 along a shaft 22, with the proximal ends 54 ofthe fingers 68 pointing toward the proximal end 31 of the shaft 22. Alocking collar 20 may then be positioned on the shaft 22 of the tap 12so that it is capable of coupling with the stop collar 18. The stopcollar 18 and the locking collar 22 are then joined together.

The tightness of the connection between the stop collar 18 and thelocking collar 20 may then be adjusted to provide a desired resistanceto movement between the stop collar-locking collar combination and thetap 12. The position of the stop collar 18 may then be adjusted to adesired tap length 28 setting by aligning the proximal ends 74 of thestop collar with the desired length indicator 26. For example, thenumeral 5 may designate the appropriate length indicator 26 for aparticular screw with a length of 5 mm. The connection between the stopcollar 18 and the locking collar 20 may then be tightened to secure theselected length 28 of the tap assembly. Alternatively, the position ofthe stop collar may be positioned to provide a desired tap length. Thestop collar 18 may be advanced to set the desired position and thelocking collar then positioned on the shaft, coupled to the stop collar,and adjusted to lock the stop collar and locking collar assembly inplace on the shaft.

The proximal end 31 of the self-drilling tap 12 may then be inserted into a drill (not shown), such as a battery powered reversible drill. Thetip 13 of the self-drilling tap 12 may be seated in a guide plate andplaced into contact with bone. The drill may then be used to rotate theadjustable length tap assembly 10 to bore and tap a hole ofpredetermined dimension into the bone. The maximum depth of the bore maybe reached when the nose 58 of the stop collar contacts the guide plate.The adjustable length tap assembly 10 may then be withdrawn from thebore and the guide plate, and a screw advanced and secured in the tappedbore.

The locking mechanism of the assembly 10 allows the stop collar 18 andlocking collar 20 to rotate with respect to the tap 12, particularlyafter the stop collar 18 hits the drill guide plate without affectingthe previously adjusted length setting 28. Because the nub 48 is firmlyseated in the groove 24, the length of the tap 28 may not change,however, the stop collar 18 and locking collar 20 are free to rotateabout the shaft 22. This may facilitate accuracy in the advancement ofbores having a pre-selected depth. For instance, if relative rotationbetween the stop collar 20 and the shaft could change the length of theexposed cutting threads 28, each time the stop collar hits the drillguide plate the resulting movement between the shaft and the stop collarmight potentially cause the tap 12 to change length 28. If the exposedlength of the cutting threads 28 was unintentionally lengthened the boremight proceed undesirably through the bone and into adjacent tissue. Bycontrast, if the exposed length of the cutting threads 28 was decreased,a screw advancing into untapped bone might damage or crack the bone orin the case of resorbable screws, damage may occur to the screw.

The tap assembly may also provide useful tactile feed back to the user,due to the ratchet effect of the nubs 48 engaging and disengaging withthe grooves 24 as the stop collar 18 and locking collar 28 are movedalong the shaft 22. A user may feel and hear the number of clicks as thenubs disengage and engage grooves as the stop collar translates alongthe shaft from a first known tap length setting to a desired second taplength setting, thereby increasing the speed of tap adjustments during aprocedure. In addition, the ratchet effect of the locking mechanism mayprovide an additional check for assuring the proper length is selectedas the user need not rely on a purely visual system to select or checkthe length adjustment of the tap assembly.

While the above adjustable length tap assembly has been described withreference to certain preferred embodiments, it should be kept in mindthat the scope of the present invention is not limited to theseembodiments. For instance, the adjustable length tap assembly may bemodified or extended to accommodate particular formulations ofconstruction materials or fabrication techniques which may requiredifferent connecting elements. Similarly, the number and spacing of thegrooves on the shaft may be changed to accommodate different screwlengths. Also, different materials and surface coatings, or outer layersof different materials may be applied to the adjustable length tapassembly. In addition, the embodiments above can be modified so thatsome features of one embodiment are used with the features of anotherembodiment. One skilled in the art may adapt variations of thesepreferred embodiments which, nevertheless, fall within the spirit of thepresent invention, whose scope is defined by the claims set forth below.

1. An adjustable length tap assembly for drilling holes in bonecomprising: a shaft having a length along a longitudinal axis andincluding cutting threads configured for drilling holes in bone; and astop collar positionable around the shaft and rotatable about thelongitudinal axis in a locked configuration and an unlockedconfiguration, the stop collar being fixed at a location along thelength of the shaft in the locked configuration and being moveable alongthe length of the shaft in the unlocked configuration.
 2. The adjustablelength tap assembly of claim 1, further including a length scale havingindicator markings to show a selectable exposed tap length.
 3. Theadjustable length tap assembly of claim 2, wherein the indicatormarkings are length numbers.
 4. The adjustable length tap assembly ofclaim 2, wherein the indicator markings indicate a specific screw type.5. The adjustable length tap assembly of claim 1, wherein the stopcollar includes a projection configured to engage a portion of the shaftto fix the location of the stop collar along the length of the shaft inthe locked configuration.
 6. The adjustable length tap assembly of claim5, wherein the shaft includes a plurality of circumferential grooves,and wherein the projection is configured to engage one of the pluralityof circumferential grooves in the locked configuration.
 7. Theadjustable length tap assembly of claim 6, further including a lockingcollar positionable around the stop collar and configured to transitionthe stop collar between the unlocked configuration and the lockedconfiguration.
 8. The adjustable length tap assembly of claim 7, whereinthe locking collar is configured to push the projection into one of theplurality of circumferential grooves.
 9. The adjustable length tapassembly of claim 5, wherein the projection is integrally formed as apart of the stop collar.
 10. An adjustable length tap assembly forthreading holes in bone comprising: a shaft, including cutting threadsfor threading holes in bone; a number of circumferential grooves arounda portion of the shaft; a stop collar that is moveable along a length ofthe shaft; a selectably engageable projection to engage both the shaftand the stop collar to fix a location of the stop collar along thelength of the shaft; wherein the stop collar is free to rotate withrespect to the shaft when fixed at a selected location along the lengthof the shaft.
 11. The adjustable length tap assembly of claim 10,further including a locking collar to actuate the engageable projectioninto one of the number of circumferential grooves.
 12. The adjustablelength tap assembly of claim 11, wherein the locking collar is actuatedby rotating a threaded locking collar into contact with a portion of thestop collar.
 13. The adjustable length tap assembly of claim 10, furtherincluding a length scale having indicator markings to show a selectableexposed tap length.
 14. The adjustable length tap assembly of claim 13,wherein the indicator markings are length numbers.
 15. The adjustablelength tap assembly of claim 13, wherein the indicator markings indicatea specific screw type.